Belt drives of the kind described above are well known and provide a drive to be affected over a large spatial distance using simple means. The belt drives can also be used as a controlling drive because the belt provides for a definite coordination of the position of the driven parts to the parts of the drive shaft.
The belt pulley has a supporting surface for the belt laterally of the projections especially for thin perforated drive belts. This bearing surface is a part of the wheel which is driven or which performs the driving and has the above-mentioned projections.
Published German patent application DE 34 18 383 discloses a belt pulley for such a belt drive. Forms and dimensions of the projections and of the supporting surface are given which are intended to act advantageously with respect to the running characteristics of the drive. Projections having round lateral boundary faces are especially preferred.
Published international patent application with International Publication Number WO 86104570 discloses possibilities as to how a second belt pulley can be advantageously configured. The second belt pulley is driven with such a belt drive and has a larger diameter than the driving pulley.
In the known belt drives of this kind, the belt is driven simultaneously by two mechanisms. The first driving mechanism takes place by means of the engagement of the projections of the belt pulley in the cutouts or perforations of the belt. This drive mechanism constitutes a positive belt drive. The friction between the supporting surface and the belt constitutes a second competing drive mechanism. Because of expansion slippage, the second drive mechanism drives the belt faster via the supporting surface than the positive first drive mechanism.
High stresses occur at the perforations in the belt as a consequence of these two competing drive mechanisms having different transport velocities. This stress damages the perforations on the side opposite to the direction of movement of the belt and can lead to a destruction of the belt. This problem occurs, for example, in photogrammetric apparatus. There, thin perforated steel bands drive the focal plane shutter of the camera and damage to these belts can lead to a premature malfunction of the apparatus.